1. Field of the Invention
The present invention relates to sliding members having a sliding surface for sliding contact with a cooperative member, such as inner and outer blades of an electric shaver, compressor parts, VTR parts and thin film magnetic heads. The present invention further relates to a method of forming a film on a substrate by utilizing a CVD method.
2. Description of Related Art
Investigations have been made as to the formation of a protective film, such as a nitride or diamond-like carbon film, on a skin-contacting, outer surface of an outer blade of an electric shaver, which can impart improved wear-resistance thereto. However, the formation of protective film on an inner surface of the outer blade, which is brought into contact with an inner blade of the electric shaver, has not been put into general practice up to date. Likewise, the formation of protective film on an sliding surface of a distal edge of the inner blade of electric shaver, which is brought into contact with the outer blade, has not been put into general practice up to date.
The inventors of the present application have investigated to what extent wear-resistance can be improved by providing a protective film, such as a diamond-like carbon film, on a sliding surface of an inner or outer blade of an electric shaver, and found that such formation of protective film on the sliding surface results in delamination thereof from the sliding surface or in cutout thereof at the edges of sliding surface, which causes wear of the sliding surface.
Such occurrence of delamination or cutout of the protective film is not limited to the cases where it is applied to the inner or outer blade of an electric shaver, and can also be found in the cases where it is applied onto sliding surfaces, such as of sliding parts of compressor, sliding members of VTR and thin film magnetic heads.
For these sliding members, a protective film is sought which exhibits reduced amount of wear and excellent sliding characteristics.
A plasma CVD method, which deposits a film by decomposing a source gas in a plasma, has been widely used as a measure of forming a film at a relatively low temperature, and is capable of forming films having various compositions by suitably selecting the source gas. Such a CVD method can be utilized to form various films, such as diamond-like carbon films having high degrees of hardness, carbon nitride (CN) and carbon silicide (CSi) films respectively having low levels of friction coefficient.
For example, a diamond-like carbon film, when formed on a silicon substrate, shows a good adhesion to the silicon substrate. However, when attempted to form a carbon nitride or carbon silicide film on the silicon substrate by using conventional film-forming techniques, there arises a problem of poor adhesion therebetween.
A first object of the present invention is to prevent delamination or cutout of a protective film provided on a sliding surface of a sliding member.
A second object of the present invention is to provide a sliding member carrying on its sliding surface a protective film which exhibits a reduced level of wear and is excellent in sliding characteristics.
A third object of the present invention is to provide a method of forming a film which is as highly functional as a carbon nitride or carbon silicide film and which exhibits good adhesion to a substrate by utilizing a plasma CVD method.
A sliding member in accordance with a first aspect of the present invention is the sliding member having a sliding surface for sliding contact with a cooperative member. A protective film is deposited over the sliding surface and a surface region immediately adjacent the sliding surface in such a characteristic manner that a ratio d1/d2 is controlled to be less than 1, wherein d1 is a thickness of the protective film overlying the sliding surface and d2 is a thickness of the protective film overlying the surface region immediately adjacent the sliding surface.
In a first preferred embodiment according to the first aspect of the present invention, the sliding member is an inner blade of an electric shaver. That is, the electric shaver inner blade of this embodiment has at its distal end a sliding surface for sliding contact with an outer blade of the electric shaver. A protective film is deposited not only on the sliding surface but also on side regions of the inner blade immediately adjacent the sliding surface, in such a characteristic manner that a ratio d1/d2 is controlled to be not less than 1, wherein d1 is a thickness of the protective film overlying the sliding surface and d2 is a thickness of the protective film overlying the side regions.
In a second preferred embodiment according to the first aspect of the present invention, the sliding member is an outer blade of an electric shaver. That is, the electric shaver outer blade of this embodiment defines a sliding surface, which is brought into sliding contact with an electric shaver inner blade, on its inner surface region around a hole for catching the beard. The outer blade carries the protective film not only on its sliding surface but also on an outer surface region around the hole in such a characteristic manner that a ratio d1/d2 is controlled to be not less than 1, wherein d1 is a thickness of the protective film overlying the sliding surface and d2 is a thickness of the protective film overlying the outer surface region.
In the first aspect of the present invention, the region immediately adjacent the sliding surface refers to the region which extends from an edge of the sliding surface at least a distance corresponding in dimension to the thickness of the protective film overlying the sliding surface.
In the first aspect of the present invention, the aforementioned thickness ratio d1/d2 is not less than 1, as specified above, preferably in the range of 1.05xcx9c5.0, more preferably in the range of 1.1xcx9c3.3.
The deposition of the protective film not only on the sliding surface but also on the region immediately adjacent the sliding surface, in accordance with the first aspect of the present invention, effectively prevents the occurrence of delamination or cutout of the protective film. If the thickness d2 of protective film, either deposited on the side regions immediately adjacent the sliding surface of the electric shaver inner blade, or deposited on the outer surface region of the electric shaver outer blade around the hole for catching the beard, is controlled to fall within the above-specified range, the delamination or cutout of the protective film on the sliding surface of either member can be prevented, while either member can maintain its function as a sliding member.
In the first aspect of the present invention, the thickness ratio d1/d2 of the protective films is controlled to fall within the range as specified above. The thickness d1 of protective film on the sliding surface is suitably selected depending on the particular uses of sliding members, but is generally preferred to fall within the approximate range of 50 xc3x85xcx9c10 xcexcm.
In the first aspect of the present invention, the hardness of protective film is preferably not less than 1000 Hv, more preferably not less than 1500 Hv.
A sliding member in accordance with the second aspect of the present invention is the sliding member having a sliding surface for sliding contact with a cooperative member. The sliding member carries a protective film at least on its sliding surface. Characteristically, the protective film is varied in thickness to have projected and depressed portions which together define an irregular surface profile.
In the second aspect of the present invention, the projected and depressed portions of the protective film may be arranged in either regular or irregular pattern. For example, the projected and depressed portions of the protective film may be alternatingly arranged to provide a striped pattern on the surface of the protective film.
In the second aspect of the present invention, the difference in height between the neighboring projected and depressed portions is not particularly specified, but may be in the range of 100xcx9c1000 xc3x85. In a particular case where the electric shaver outer blade is selected as the sliding member, a center distance between the neighboring projected and depressed portions of the protective film may be about 1xcx9c3 mm, for example.
In the second aspect of the present invention, the different color tones can be imparted to the projected and depressed portions of the protective film by using as the protective film a transparent film which, due to optical interference, assumes different color tones depending on its thickness. The wear of protective film generally progresses at its projected portions brought into direct contact with a cooperative member. As these projected portions wear to get thinner, their color tone is caused to change. Accordingly, the degree of wear of the protective film can be identified by visually observing the change in color tone of such projected portions. This helps us to find the time to replace the sliding member, for example.
The second aspect of the present invention may incorporate the first aspect of the present invention. That is, when the protective film is deposited not only on the sliding surface but also on the region immediately adjacent the sliding surface, the thickness ratio d1/d2 may be controlled to be not less than 1 wherein d1 is the thickness of the protective film on the sliding surface and d2 is the thickness of the protective film on the region immediately adjacent the sliding surface. In this instance, the irregular surface profile may be imparted at least to the protective film on the sliding surface.
In the following description, the matters common to the first and second aspects of the present invention may be referred to as those of xe2x80x9cthe present inventionxe2x80x9d.
Exemplary of the protective film are hard carbon films comprised of diamond and/or amorphous carbon having a diamond structure, and ceramic films.
Specific examples of the hard carbon films include a crystalline diamond film, an amorphous diamond-like carbon film and a diamond-like carbon film partly containing a crystalline structure. The hard carbon film of the present invention may contain the other elements, such as nitrogen and Si, in a mixed fashion.
Examples of the ceramics for use in the protective film of the present invention include oxides, nitrides and carbides of Zr, Ti, Cr, Hf, B, C, Ta, Al and Si.
Other than the aforementioned hard carbon films and ceramic films, metal films such as of Cr and Ni can also be used for the protective film. Such metal films can be formed by plating, for example.
The protective film of the present invention can be formed as by an ECR plasma CVD method and an ion beam deposition method. Other applicable methods include sputtering methods, the other types of PVD and CVD methods, and plating.
The protective film of the present invention may be deposited on an interlayer which has been deposited to cover the sliding surface and the surface region immediately adjacent the sliding surface of the sliding member. The thickness of the interlayer on the sliding surface is preferably made about comparable to that on the surface region immediately adjacent the sliding surface. However, they may be differentiated from each other. The thickness of the interlayer is preferably in the approximate range of 50 xc3x85xcx9c8000 xc3x85.
The sliding member of the present invention is illustrated as the electric shaver inner blade in the first embodiment and as the electric shaver outer blade in the second embodiment. However, the sliding member of the present invention can also be applied to the other sliding members, e.g., parts of a compressor such as a rotary compressor. Specifically, the present invention can be applied to rotary compressor parts including a roller, cylinder, vane, and a member having channels for receiving the cylinder. The present invention is also applicable to sliding parts of a VTR, and a thin film magnetic head for use in a hard disk drive (HDD). The present invention is further applicable to a sliding member such as a mask screen which is used to locate a solder at a target position when electronic parts are mounted on a printed circuit board.
The material type of the sliding member in the present invention is not particularly limited, and may be stainless steel, iron-based alloys, cast irons (Moxe2x80x94Nixe2x80x94Cr cast iron), steel (high-speed tool steel), aluminum alloys, carbons (aluminum-impregnated carbons), ceramics (oxides, nitrides, or carbides of Ti, Al, Zr, Si, W and Mo), Ni alloys, Ti alloys, or super hard alloys (WC, TiC, or BN), for example.
A method in accordance with a third aspect of the present invention is the method which deposits a film having a thickness varied in a manner to define an irregular surface by using a CVD technique. This method is characterized as comprising the steps of providing a distribution of lines of magnetic force above the substrate, and depositing the film on the substrate so that the film is varied in thickness in a pattern corresponding to the distribution of lines of magnetic force to define said irregular surface.
Although not intended to limit the scope of the present invention, the method in accordance with the third aspect of the present invention may be employed to form the protective film of the sliding member in accordance with the second aspect of the present invention.
In the third aspect of the present invention, the distribution of lines of magnetic force can be produced above the substrate by using various techniques. For example, it can be produced by placing a magnet beneath the substrate. In this instance, the substrate, if magnetic, can be fixed in position by the magnet.
A method in accordance with a fourth aspect of the present invention is also the method which deposits a film having a thickness varied in a manner to define an irregular surface by using a CVD technique. This method is characterized as comprising the steps of depositing a first film on selected regions of a substrate, and depositing a second film over an entire surface of the substrate carrying the first film so that a film comprising the first and second films can be produced which is varied in thickness to have relatively thick portions corresponding in location to said selected regions for defining said irregular surface.
Although not intended to limit the scope of the present invention, the method in accordance with the fourth aspect of the present invention may be employed to form the protective film of the sliding member in accordance with the second aspect of the present invention.
In the fourth aspect of the present invention, the deposition of first film on the selected-regions of the substrate can be accomplished, for example, by using a mask which functions to confine the deposition of first film on the selected regions of the substrate.
Examples of the film deposited in accordance with the third and fourth aspects of the present invention include hard carbon films comprised of diamond and/or amorphous carbon having a diamond structure, and ceramic films.
A method in accordance with a fifth aspect of the present invention is the method which deposit a film on a substrate by a CVD technique utilizing a plasma. The method includes the steps of decomposing a source gas in a plasma to deposit a first film layer on the substrate, and directing ions or radicals onto the substrate, while decomposing the source gas in the plasma, to deposit a second film layer on the first film layer to thereby provide the film on the substrate.
In the fifth aspect of the present invention, the ions or radicals for use in the deposition of the second film layer may generally be of an element different in type from a principal constituent element of the source gas. If contemplated forming the first and second film layers respectively from a carbon film and a carbon nitride or carbon silicide film, for example, a gas comprised principally of carbon, such as a CH4 gas, may generally be used as the source gas and the ions or radicals of silicon or nitrogen may be directed onto the substrate. However, the ions or radicals for use in the deposition of the second film layer may be of the same element as principally constituting the source gas.
In the fifth aspect of the present invention, the applicable source gases, other than the gas comprised principally of carbon, include the gases which, as a principal component, contains silicon, titanium, zirconium, boron, hafnium, or aluminum. The applicable ions or radicals for use in the deposition of the second film layer, other than the aforementioned ions or radicals of silicon and nitrogen, include those of carbon, oxygen and hydrogen.
In accordance with the fifth aspect of the present invention, the first film layer may be made from a film which is well-adherent to the substrate, and the second film layer may be made from a film, such as a carbon nitride or carbon silicide film, which is poorly-adherent to the substrate but has desired functions. Accordingly, the deposition of such a functional, second film layer on the substrate, through the first film layer, results in the formation of a functional film showing good adhesion to the substrate.
In the film-forming method in accordance with the fifth aspect of the present invention, during the formation of the second film layer, the irradiation energy and dose of ions or radicals may be varied with film-forming time. Such variations in irradiation energy and dose of ions or radicals are effective to cause the distribution of the ion or radical component introduced into the second film layer to be varied in a thickness direction of the second film layer.
By reducing the irradiation energy of ions or radicals with film-forming time and increasing the irradiation dose of ions or radicals with film-forming time, a concentration of the ion or radical component introduced into the second film layer can be increased toward its surface so that a concentration gradient of the component is produced in the thickness direction of the second film layer.
The introduction of such a concentration gradient of the component into the second film layer imparts the improved function to the surface of the second film layer. The second film layer, if made from a carbon nitride or carbon silicide film, exhibits the reduced coefficient of friction toward its surface. The provision of the concentration gradient also results in the formation of a film which exhibits the improved adhesion to a substrate and is imparted thereto the satisfactory functions.
A film-forming method in accordance with a sixth aspect of the present invention is the method of depositing a film on a substrate by a CVD technique utilizing a plasma, and includes the steps of decomposing a source gas in a plasma to thereby deposit a first film layer on a substrate; and applying a radio-frequency power to the substrate for producing a substrate bias voltage (self-bias voltage) and concurrently irradiating the substrate with ions or radicals, while the source gas is decomposed in the plasma, to thereby deposit a second film layer on the first film layer.
In the sixth aspect of the present invention, the ions or radicals for use in the deposition of the second film layer may generally be of an element different in type from a principal constituent element of the source gas. If contemplated forming the first and second film layers respectively from a carbon film and a carbon nitride or carbon silicide film, for example, a gas comprised principally of carbon, such as a CH4 gas, may generally be used as the source gas and the ions or radicals of silicon or nitrogen may be directed onto the substrate. However, the ions or radicals for use in the deposition of the second film layer may be of the same element as principally constituting the source gas.
In the sixth aspect of the present invention, the applicable source gases, other than the gas comprised principally of carbon, include the gases which contains, as a principal component, silicon, titanium, zirconium, boron, hafnium, or aluminum. The applicable ions or radicals for use in the deposition of the second film layer, other than the aforementioned ions or radicals of silicon and nitrogen, include those of carbon, oxygen and hydrogen.
In accordance with the sixth aspect of the present invention, the first film layer may be made from a film which is well-adherent to the substrate, and the second film may be made from a film, such as a carbon nitride or carbon silicide film, which is poorly-adherent to the substrate but has desired functions. Accordingly, the deposition of such a functional, second film on the substrate, through the first film, results in the formation of a functional film showing good adhesion to the substrate.
Also in the film-forming method in accordance with the sixth aspect of the present invention, during the formation of the second film layer, the irradiation energy and dose of ions or radicals, as well as the substrate bias voltage, may be varied with film-forming time. Such variations in irradiation energy of ions or radicals and the others are effective to cause the distribution of the ion or radical component introduced into the second film layer to be varied in a thickness direction of the second film layer.
By reducing the irradiation energy of ions or radicals and the substrate bias voltage with film-forming time and increasing the irradiation dose of ions or radicals with film-forming time, a concentration of the ion or radical component introduced into the second film layer can be increased toward its surface so that a concentration gradient of the component is produced in the thickness direction of the second film layer.
The introduction of such a concentration gradient of the component into the second film layer imparts the improved function to the surface of the second film layer. The second film layer, if made from a carbon nitride or carbon silicide film, exhibits the reduced coefficient of friction toward its surface. The provision of the concentration gradient also results in the formation of a film which exhibits the improved adhesion to a substrate and is imparted thereto the satisfactory functions.
In the sixth aspect of the present invention, the application of radio-frequency power to the substrate causes the production of negative bias voltage in the substrate, as stated above. Such a negative bias voltage, if produced, generally acts to attract positive ions to the substrate so that they are preferentially introduced into the second film layer. Accordingly, in the sixth aspect of the present invention, those positive ions, if directed onto the substrate during the deposition of second film layer, are preferentially incorporated into the second film layer.
Also in the sixth aspect of the present invention, the radio-frequency power may be applied to the substrate to produce the substrate bias voltage during the deposition of first film layer on the substrate.
A film-forming method in accordance with a seventh aspect of the present invention is the method of depositing a film on a substrate by a CVD technique utilizing a plasma, and includes the steps of decomposing a source gas in a plasma to thereby deposit a first film layer on a substrate, and decomposing the source gas, as well as a second source gas which contains an element different in type from a principal constituent element of the source gas, in the plasma to thereby deposit a second film layer on the first film layer.
In the seventh aspect of the present invention, the second film layer can be formed which contains the element different in type from the constituent component of the first film layer, by decomposing the source gas and the second source gas in the plasma. It accordingly becomes possible, for example, to form a carbon-based film as the first film layer and subsequently form a film containing an element other than carbon, such as a carbon nitride or carbon silicide film, as the second film layer. In this exemplary case, the second source gas contains nitrogen or silicon.
In the seventh aspect of the present invention, the source gas may be varied in amount with film-forming time. Such a variation in amount of the second source gas with film-forming time leads to the varied distribution in concentration of the element contained in the second source gas in a thickness direction of the second film layer. For example, the increase in amount of the second source gas results in the formation of the second film layer which has an increased concentration of the element contained in the second source gas toward its surface so that a concentration gradient thereof is produced in the thickness direction of the second film layer.
The films of the present invention can be formed by using the film-forming methods in accordance with the aforementioned fifth, sixth and seventh aspects of the present invention. That is, the film of the present invention includes the first film layer comprised of a hard carbon film, and the second film layer deposited on the first film layer and containing nitrogen or silicon as well as the constituent component of the first film layer.
In the aforementioned fifth, sixth and seventh aspects of the present invention, the film of the present invention can be obtained by forming a hard carbon film as the first film layer and subsequently forming a carbon film containing nitrogen or silicon as the second film layer.
In forming the film of the present invention, a carbon-containing gas, such as a methane gas, may be used. In the fifth and sixth aspects of the present invention, ions or radicals of nitrogen or silicon may be directed onto the substrate. In the seventh aspect of the present invention, a gas containing nitrogen or silicon may be used as the second source gas.
In the present invention, the hard carbon film for constituting the first film layer may be a crystalline diamond film, an amorphous diamond-like carbon film, or a diamond-like carbon film partly having a crystalline structure.
In the film of the present invention, the thicknesses of the first and second film layers are not particularly specified. Although not limiting, the thickness of the first film layer is generally in the range of 20 xc3x85xcx9c3000 xc3x85, and the thickness of the second film layer is generally in the range of 30 xc3x85xcx9c4 xcexcm (40,000 xc3x85).
The nitrogen or silicon content of the second film layer is preferably in the approximate range of 5xcx9c40 atomic %.
The concentration of nitrogen or silicon in the second film layer may be graded in a thickness direction thereof. In the preferred embodiment, the second film layer has such a concentration gradient in its thickness direction that the concentration of nitrogen or silicon is increased toward a surface of the second film layer.
The films formed by using the film-forming methods in accordance with the fifth through seventh aspects of the present invention, as well as the films in accordance with the present invention, may further have an interlayer interposed between the first film layer and the substrate. Such an interlayer may be formed of Si, Ti, Zr, W, Mo, Ru or Ge, or an oxide, nitride or carbide of any of thereof, for example. The interlayer can be formed by using generally-employed film-forming techniques. A magnetron RF sputtering technique, for example, can be utilized to form the interlayer. Such a sputtering technique generally uses the aforementioned metal element as a target which is sputtered by ions in argon plasmas to deposit a film. The sputtering, if accompanied by the introduction of an oxygen or nitrogen gas into a chamber, can deposit an oxide or nitride of the metal element as the interlayer. The sputtering, if accompanied by the introduction of a carbon-containing gas, such as a CH4 gas, into the chamber, can deposit a carbide of the metal element as the interlayer.
The thickness of the interlayer may be in the approximate range of 20 xc3x85xcx9c3000 xc3x85, for example.